arXiv subjects

Yu-Hao Zhang

Publications and source records attributed to Yu-Hao Zhang.

11 recordsLinked to original sources

arXiv2026

SN 2025fhm: A central-engine powered Ic-BL supernova associated with X-ray transient EP250304a

We present X-ray, optical, and radio follow-up observations of EP250304a, an extragalactic fast X-ray transient (EFXT) discovered by the Einstein Probe. Its X-ray light curve exhibits two broad pulses with comparable peak fluxes within the first $\sim$1~ks, a feature rarely seen among low-luminosity gamma-ray bursts or EFXTs. Optical follow-up observations were carried out using the Korea Microlensing Telescope Network, the Thai Robotic Telescope, the Las Cumbres Observatory 1~m global network, the Gemini Multi-Object Spectrograph on Gemini south telescope, and the Global Supernova Network. The fast-cooling phase (within 3 days) of optical data can be well fitted by a shocked cocoon model. However, during the supernova phase (SN 2025fhm, from 3 to 88 days), the late-time light curve cannot be explained solely by radioactive $^{56}$Ni decay, as demonstrated by a grid of simulations using the one-dimensional Lagrangian radiation hydrodynamics code SNEC, which reveals a significant energy excess at late epochs. To account for this excess, a central engine like a rapidly spinning, highly magnetized neutron star is needed to provide additional energy injection. This model yields a best-fit spin period of $\sim$12.60~ms and magnetic field strength of $\sim 3.52\times10^{15} \rm G$, and it successfully explains both the late-time bolometric light curve and the early X-ray pulse structures. Our results indicate that EP250304a/SN 2025fhm is likely powered by a central magnetar rather than by radioactive decay alone, offering new insights into the energy budget and physical origin of EFXTs and their associated supernovae.

astro-ph.HE↗

arXiv2026

Coupled Shock Cooling and Radioactive Heating in the Type IIb Supernova SN 2024aecx: An Extended Envelope and Rapid Optical Decline

SN~2024aecx is a nearby, rapidly evolving stripped-envelope supernova with a prominent double-peaked ultraviolet--optical light curve. We model its multiband evolution with an extended version of \texttt{TransFit}, in which the early shock-cooling emission and the subsequent radioactive heating are treated within a single time-dependent radiative diffusion calculation. To describe the stratified ejecta expected for a Type~IIb progenitor, we adopt a compact inner ejecta connected to a dilute extended outer envelope and fit the outer density slope directly from the early light curve. The model reproduces the short-lived first peak, the rise to the radioactive main peak, and the overall multiband evolution. We infer an effective outer radius of $R_0=109.6^{+6.6}_{-3.5}\,R_\odot$, an ejecta mass of $M_{\rm ej}=2.14^{+0.21}_{-0.19}\,M_\odot$, a nickel mass of $M_{\rm Ni}=0.050\pm0.002\,M_\odot$, and a steep outer density slope of $n_{\rm out}=13.33^{+0.11}_{-0.12}$. The steep outer profile favors a low-mass extended envelope, while the low ejecta mass explains the rapid evolution of the main peak. However, a control model with standard $γ$-ray leakage fades too slowly after maximum. We therefore introduce an effective optical-output factor to quantify the additional late-time suppression of the ultraviolet--optical luminosity. These results support the shock-cooling plus radioactive-heating interpretation of SN~2024aecx, but show that its rapid optical decline requires physics beyond the simplest radioactive-diffusion prescription.

astro-ph.HE↗

arXiv2026

X-rays breaking out of pre-explosion ejecta mark a supernova's first light

Massive stars die as core-collapse supernovae, whose optical light emerges days after the implosion. Theory predicts that the initial collapse-driven shock, upon breaking through the star and dense circumstellar medium, emits a brief thermal flash of soft X-rays and ultraviolet. Yet these elusive first signals have remained largely undetected, owing to limited wide-field soft X-ray monitoring. Here we report the discovery of a soft X-ray flash, EP260321a, followed days later by a broad-lined supernova from an envelope-stripped progenitor. Its X-ray spectrum, best modeled with blackbody, establishes it as the long-sought archetypal shock breakout. The burst's duration and energetics place the breakout at a radius of 300 solar radii, tracing a dense surrounding shell and revealing abrupt mass ejection within the final month before collapse.

astro-ph.HE↗

arXiv2026

Mapping the Dense Circumstellar Environments of SNe Ibn, SNe Icn, and Fast Blue Optical Transients

SNe Ibn and SNe Icn are stripped-envelope explosions whose optical emission is commonly linked to interaction with H-poor circumstellar material (CSM), whereas fast blue optical transients (FBOTs) form an observational class of rapidly evolving, blue, and luminous events with diverse proposed power sources. We present a uniform comparison of these transients to test whether they are separated in optical light-curve and fitted physical parameter space. We compile multiband optical light curves of 25 SNe Ibn, SNe Icn, and FBOTs, measure same-band observables with Gaussian-process reconstructions, and model the data with the unified \texttt{TransFit-CSM} framework. In the observed (g)-band peak-luminosity--rise-time and decline--rise-time planes, the three classes are not cleanly separated: FBOTs preferentially occupy the luminous and rapidly evolving end of the distribution, but show limited overlap with part of the Ibn/Icn population. Their extinction-corrected peak colors span a broadly overlapping blue region, with FBOTs extending to bluer colors. Unified CSM-interaction fits, including shock heating and an effective inner heating component, yield overlapping CSM and ejecta parameter distributions. These results indicate that the optical light curves of SNe Ibn, SNe Icn, and at least some FBOTs can be compared within a common dense-CSM interaction framework, while the most extreme FBOTs may still require additional power sources or non-thermal components.

astro-ph.HE↗

arXiv2026

\texttt{TransFit-MAG}: Self-Consistent Modeling of Magnetar-Powered Transients from Shock Breakout to Spin-Down Heating

Magnetar engines are widely invoked to power luminous optical transients, but their early emission depends on the coupled evolution of engine injection, shock heating, adiabatic cooling, and radiative diffusion. We present \texttt{TransFit-MAG}, a time-dependent radiative-diffusion framework for magnetar-powered transients. The model couples the \texttt{TransFit} diffusion solver to the dynamics of a magnetar-inflated pulsar wind nebula (PWN) and its forward shock propagating through homologously expanding ejecta, calculating the internal radiation-energy distribution, photospheric evolution, shock-heating location, and emergent luminosity self-consistently. For different parameter values, the model naturally produces well-separated double peaks, partially merged peaks, or single broad peaks. These results suggest that early bumps and broad single peaks in engine-powered transients may be understood within a unified engine--shock--diffusion framework, in which the observed diversity reflects the coupled evolution of central-engine power, shock propagation, and radiative transport through expanding ejecta. As an illustrative application, we fit the multiband optical light curves of the double-peaked SLSN-I LSQ14bdq.

astro-ph.HE↗

arXiv2026

WFST Supernovae in the First Year: III. Systematical Study of the Photometric Behavior of Early-phase Core-collapse Supernovae

We investigate the multiband photometric properties of seven supernovae (SNe) showing double-peaked light-curve evolution and prominent shock-cooling emission, observed by the Wide Field Survey Telescope (WFST) during its first year of operation. By jointly employing an analytic early shock-cooling model and the Arnett radioactive-diffusion model, we fit the bolometric light curves and infer ejecta masses in the range $1.1$-$2.6 M_\odot$, consistent with a transitional population between ultra-stripped supernovae (USSNe) and normal stripped-envelope supernovae (SESNe). The envelope masses are estimated to be $M_{\rm env}=0.1$-$0.4 M_\odot$, while the progenitors are constrained to be yellow or blue supergiants (YSGs/BSGs) with radii of $R=120$-$300 R_\odot$. Using empirical relations, we estimate progenitor luminosities of $L=10^{4.6}$-$10^{4.9} L_\odot$, corresponding to zero-age main-sequence (ZAMS) masses of $8$-$20 M_\odot$. Theoretical models suggest that such progenitors are more naturally produced through binary evolution channels, as single-star evolutionary pathways are unable to yield ejecta masses this low.

astro-ph.HE↗

arXiv2025

SN 2024aecx: a fast-evolving Type IIb supernova with a prominent shock-cooling peak

SN 2024aecx is a nearby ($\sim$11 Mpc) Type IIb SN discovered within $\sim$1 d after explosion. In this paper we report high-cadence photometric (typically 0.5$\sim$1 day) and spectroscopic follow-up observations, conducted from as early as 0.27 d post discovery out to the nebular phase at 158.4 d. We analyze the environment of SN 2024aecx and derive a new distance (11.3$\pm$1.1 Mpc), metallicity and host extinction. The light curve exhibits a hot and luminous shock-cooling peak at the first few days, followed by a main peak with very rapid post-maximum decline. The earliest spectra are blue and featureless, while from 2.3 d after discovery prominent P-Cygni profiles emerge. At nebular phase, the emission lines exhibit asymmetric and double-peaked profiles, indicating asphericity and/or early dust formation in the ejecta. Nebular spectral modelling indicates a blueshifted O-rich clump moving toward observer, and the $[\text{OI}]/[\text{CaII}]$ line ratio suggests an intermediate-mass progenitor. We simulated the progenitor and explosion using a two-component model of shock cooling and radioactive $^{56}$Ni heating; our model favors an extended, low-mass H-rich envelope with $M_{\mathrm{e}} = 0.04\pm{0.01} M_{\odot}$ and a low ejecta mass of$M_{\mathrm{ej}} = 1.55^{+0.18}_{-0.14} M_{\odot}$. And the nebular-phase spectra and light-curve modelling both suggest that it most likely originated from an intermediate-mass binary progenitor system. The comprehensive monitoring of SN 2024aecx, coupled with the detailed characterization of its local environment, establishes it as a benchmark event for probing the progenitors and explosion mechanisms of Type IIb SNe.

astro-ph.SR↗

arXiv2025

TransFit-CSM: A Fast, Physically Consistent Framework for Interaction-Powered Transients

We present TransFit-CSM, a fast and physically consistent framework for modeling interaction-powered transients. The method self-consistently couples the ejecta circumstellar medium (CSM) shock dynamics to radiative diffusion from a moving heating boundary tied to the shocks, so that both the photon escape path and the effective diffusion time evolve with radius and time. We solve the mass and momentum equations for the forward and reverse shocks together with the diffusion equation in the unshocked CSM. TransFit-CSM reproduces the canonical sequence of an early dark phase, a diffusion-mediated rise and peak, and a post-interaction cooling tail, and it clarifies why Arnett-like peak scalings break down in optically thick CSM. The framework is well suited for Bayesian inference and constrains physical parameters of the ejecta and CSM from bolometric or joint multi-band light curves. Applications to SN 2006gy and SN 2010jl yield accurate fits and physically interpretable posteriors, highlighting the dominant role of pre-supernova mass loss in shaping the observables. Because it is both computationally efficient and physically grounded, TransFit-CSM bridges simple analytic prescriptions and radiation-hydrodynamic simulations, enabling population-level inference for current and future time-domain surveys.

astro-ph.HE↗

arXiv2025

TransFit: An Efficient Framework for Transient Light-Curve Fitting with Time-Dependent Radiative Diffusion

Modeling the light curves (LCs) of luminous astronomical transients, such as supernovae, is crucial for understanding their progenitor physics, particularly with the exponential growth of survey data. However, existing methods face limitations: efficient semi-analytical models (e.g., Arnett-like) employ significant physical simplifications (like time-invariant temperature profiles and simplified heating distributions), often compromising accuracy, especially for early-time LCs. Conversely, detailed numerical radiative transfer simulations, while accurate, are computationally prohibitive for large datasets. This paper introduces TransFit, a novel framework that numerically solves a generalized energy conservation equation, explicitly incorporating time-dependent radiative diffusion, continuous radioactive or central engine heating, and ejecta expansion dynamics. The model accurately captures the influence of key ejecta properties and diverse heating source characteristics on light curve morphology, including peak luminosity, rise time, and overall shape. Furthermore, TransFit provides self-consistent modeling of the transition from shock-cooling to $^{56}$Ni}-powered light curves. By combining physical realism with computational speed, TransFit provides a powerful tool for efficiently inverting LCs and extracting detailed physical insights from the vast datasets of current and future transient surveys.

astro-ph.HE↗

arXiv2016

Three-generation neutrino oscillations in curved spacetime

Three-generation MSW effect in curved spacetime is studied and a brief discussion on the gravitational correction to the neutrino self-energy is given. The modified mixing parameters and corresponding conversion probabilities of neutrinos after traveling through celestial objects of constant densities are obtained. The method to distinguish between the normal hierarchy and inverted hierarchy is discussed in this framework. Due to the gravitational redshift of energy, in some extreme situations, the resonance energy of neutrinos might be shifted noticeably and the gravitational effect on the self-energy of neutrino becomes significant at the vicinities of spacetime singularities.

hep-ph↗

arXiv2016

Self-regular black holes quantized by means of an analogue to hydrogen atoms

We suggest a quantum black hole model that is based on an analogue to hydrogen atoms. A self-regular Schwarzschild-AdS black hole is investigated, where the mass density of the extreme black hole is given by the probability density of the ground state of hydrogen atoms and the mass densities of non-extreme black holes are given by the probability densities of excited states with no angular momenta. Such an analogue is inclined to adopt quantization of black hole horizons. In this way, the total mass of black holes is quantized. Furthermore, the quantum hoop conjecture and the Correspondence Principle are discussed.

hep-th↗